A group of 24 pregnant rhesus monkeys have been maintained on one of three purified diets throughout pregnancy. One diet was restricted in protein, one deficient in both protein and calories and one was the control diet. The monkeys were delivered at 158 days of gestation by cesarean section. The fetuses were killed at time of delivery and all organs weighed and anthropometric measurements taken. Analysis of anthropometric data did not show significant differences between the fetuses taken from mothers on various diets. Furthermore analysis of chemical determinations of the cerebrum and cerebellum from fetuses of monkeys on the diets revealed no statistically significant changes in these tissues. These results indicate that the fetus of the Rhesus monkey is protected during frank protein-calorie restriction of the mother.